1. Technical Field of the Invention
The present invention relates to a threading apparatus for magnetic tape which carries a leader block provided at the end of a recording medium in a tape form from a cartridge for the recording medium to a machine reel through a threading arm, and returns the leader block to the cartridge when the medium is wound off from the machine reel.
2. Description of the Prior Art
A threading arm of a conventional magnetic tape apparatus is generally driven through gears by means of a driving motor in a threading mechanism for carrying a leader block of a recording medium in a tape form from a cartridge for the recording medium to a machine reel. The driving power becomes maximum, when the leader block is latched with a pin of the threading arm or held by means of the pin and is threaded at the position where the leader block is stopped in the cartridge and the machine reel. Further, it is necessary to stop the threading arm, when the leader block stops after carrying the leader block to the stop position
However, in view of the performance of the motor, it is impossible to start the driving of the driving motor at the above-mentioned stop position and immediately give the maximum power to the threading arm. The driving motor and the threading arm are worked together, so that it is necessary to stop the driving motor when the leader block reaches the stop position. However, when the threading arm is suddenly stopped, the position thereof is checked with a position sensor and subsequently the driving motor is stopped. Therefore, a little time lag is caused, and impact force is applied to the gears, which constitute a power transmission system. For this reason, in order to keep the strength of the gears, it is necessary to subject the gears to hardening or the like for increasing the size, the thickness or the hardness of the gears. Thus, it is difficult to make the gears small-sized, and costs increase.
There is known a mechanism wherein an elastic mechanism or an elastic material is fitted to the middle of a threading arm to relieve impact force, as shown in a given mechanism disclosed in JP 04-076849 A (1992). However, in order to move the elastic mechanism only in the axial direction of the threading arm, it is essential to use an additional mechanism such as a slide axis and a straight bearing. Thus, costs of this mechanism increase. In order to simultaneously attain the ensuring of driving power upon the latch of the leader block and the relief of the impact force upon the sudden stop thereof at the stop position in the cartridge or the machine reel, the arrangement thereof undergoes considerable restriction. Thus, it is difficult to solve this problem.
An object of the present invention is to provide a threading mechanism in a magnetic tape machine, making it possible to obtain sufficient driving power when the threading mechanism, which is for carrying a leader block in a recording medium in a tape form from a cartridge for the recording medium to a machine reel at the side of the machine, causes the leader block to be held by means of the threading arm or be kept at the threading arm; and making it possible to avoid impact force from a driving motor in spite of sudden stop of the threading arm at the above-mentioned stop position.
Therefore, the present invention is a threading mechanism in a magnetic tape machine, made so as to supply a leader block arranged at the end of a recording medium in a tape form from a cartridge for the recording medium to a machine reel through a threading arm, and so as to conversely return the leader block to the cartridge when the medium is wound off from the machine reel, characterized in that the threading arm is made so that positions where the leader block is stopped in the cartridge and the machine reel are inside a track of the threading arm which swings around its pivoting point and the leader block is threaded therebetween, and a driving arm for swinging the threading arm has a structure motor-driven around a pivoting point of the driving itself, causes the threading arm to work together between the positions where the leader block is stopped, and cancels the working with the threading arm in the direction of the trace over the stop positions, so as to be swung.
In this case, as embodiments of the present invention, the following structures are effective: a cam groove is made in the threading arm, a guide pin provided to the driving arm is inserted into the cam groove, the two are engaged with each other in the swinging direction of the threading arm between the leader block stop positions, in a trace over the stop positions, a disengaging area for canceling the engagement with the guide pin is formed; the disengaging area is made by a groove portion extending along the direction tangential to the rotation radius of the driving arm from the guide pin; position sensors are provided to a body of the machine, corresponding to the stop positions, respectively, and when the driving arm is operated in the direction of the trace over the stop positions, the position sensors function so that motor-driving of the driving arm is stopped; and the motor for operating the driving arm is a motor with an encoder, and pulses from the encoder are managed to control speed of the driving arm or to reduce the speed at the stop positions.
Accordingly, at the time of latching with the leader block, the leader block beforehand receives rotating power of the driven driving motor, so that sufficient power can be obtained. At the time of sudden stop of the threading arm at the stop positions, it is possible to obtain an effect that impact force based on the driving motor can be avoided.
According to the present invention, a first effect thereof is that impact force is not applied to the threading mechanism, the driving power transmission system connected to the driving motor, for example, gears such as reduction gears. For this reason, endurance of the machine can be improved.
A second effect thereof is that driving torque of the driving motor can be made small. This is because when the operation of the threading arm starts at the position to which the maximum load is applied in the threading mechanism, that is, at the leader block stop position, the movement of the driving arm has a play so that the rotation speed of the driving motor can be beforehand raised.
Furthermore, a third effect thereof is that the threading mechanism can be made small-sized at lower costs. This is because the motor torque can be reduced as described above so that excessive load is not applied to a power transmission system such as gears.